This invention relates generally to electrical machines such as motors and generators, and more particularly to insulation for electrical machines.
Locomotives are commonly provided with a diesel engine or other prime mover that drives a traction alternator to generate electrical current. The current from the alternator is supplied to traction motors which drive the locomotive. The traction alternator has a rotor carrying a plurality of coils that turn inside a stator. These coils must be insulated to prevent surface tracking, which can lead to alternator failure.
Varnishes with different cure characteristics are widely used in the electric machine industry as electrical insulation for rotor coils. Air-dry and room-temperature-cure catalyzed varnishes are known and have been applied to coils using a brush-on method. Varnish applied using this method can take a long time to cure and can run off, causing bare spots on the coils.
Another known insulation process is tank dipping, in which a finished rotor is submerged into bake-cure varnish, and then transferred to an oven and baked for several hours at high temperature to cure the varnish. This process requires several crane operations, a large varnish tank and oven, and a substantial amount of energy to finish the varnish cure.